<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        /* 让内联元素和内联块元素水平居中
        1.display:block;margin-left:auto;margin-right:auto;
        2.给他的父元素text-align:center;
         */
         body{
             text-align: center;
         }
    </style>
</head>
<body>
    <button>btn</button> <br>
    <a href="#">a</a>
</body>
</html>